A wide variety of pressure indicating devices have been known for some time, the majority being devices that provide a means to accurately measure pressure, particularly of gases and liquids.
In certain situations, a precise measurement of pressure is not required but rather a simple and clear indication of a change in pressure is desired, for example to detect leakage from a pressurized container. In such situations, a device that provides a highly visual “see-at-a-glance” indication that leakage is occurring is more appropriate than a precise numerical measurement of the pressure within the container.
Such devices are well known in the art. For example, a device is known for indicating whether a pneumatic circuit is pressurized, available under the trademark ROTOWINK (ex Norgren Martonair Limited). This device is adapted to be mounted on a control panel, with the inlet connected to part of a pneumatic circuit, e.g. a pressure vessel, such as a compressor reservoir. The device contains a flexible, impermeable diaphragm that spans the inlet. The diaphragm supports a spring returnable piston.
A rod and crank arrangement extends from the piston, terminating in the head of the device, remote from the inlet, where the rod is attached to a crank within a rotatable ball having its opposite halves different colors, e.g. red and green. The ball is mounted beneath a lens through which one side of the ball is clearly visible from the exterior of the device.
A difference in pressure across the diaphragm, e.g. resulting from a build up of air pressure in a compression chamber to which the inlet of the device is connected, causes the diaphragm to flex towards the head of the device, which pushes the piston and rod towards the head. This movement causes the crank to cause the ball to rotate such that the other side of the ball is then visible through the lens. This other ball side of contrasting color provides a clear visual signal that pressure has built up in the chamber.
It is highly desirable for vehicle tires to remain at their optimum pressure for reasons of safety, fuel economy and comfort and to prolong the life of the tires. Consequently, it is preferable that tire pressures are checked at regular intervals. However, this mundane task is frequently overlooked since a lower than optimal tire pressure, such as caused by a slow puncture or an inaccurate gauge on a pump or compressed air supply unit, is only perceived when the tire looks dangerously flat and/or the vehicle feels uncomfortable, at which stage the tire pressure is well below its optimum. Clearly, in the period between initial loss of air pressure and detection, any use of the vehicle reduces the life of the tire significantly and will have put the driver and passengers of the vehicle at some risk.
Although it occurs less often, it is also potentially dangerous to drive a vehicle with one or more of its tires grossly over inflated rather than under inflated.
As evidence of the long-felt need of the motoring public for a solution to these problems, one need only review the number of patents claiming to address this expensive and potentially dangerous situation. Numerous devices have been proposed and patented for providing a continuous and visible indication of tire operating pressure. Most of the prior art designs either replace the standard tire valve stem or are a replacement for the original valve cap (utilizing the existing standard valve stem). Given that the vast majority of car or truck owners would more readily replace a tire valve cap than a tire valve stem, attention will be directed towards the former. A partial list of United States Patents for devices for monitoring tire pressure is: U.S. Pat. Nos. 5,641,902; 5,569,849; 5,557,256; 5,115,832; 5,007,365; 4,819,686; 4,606,391; 4,464,929; 4,174,673, 4,116,157, 4,103,549, and 3,889,530.
In response to the numerous disadvantages of the prior art, the present invention is disclosed incorporating new and novel visual indication features.